Heretofore, the emulsion has been applied by vertically slidable squeegees of a bucket type contacted at their front edges with the screen consisting of a material such as silk, polyester, nylon or the like and having a given mesh size and a frame surrounding the material. In this case, the manual moving operation requires a particularly high skill in order to apply a film of a uniform thickness. In order to overcome the difficulty of the prior art, there have been proposed various types of mechanically moving squeegees, as disclosed in U.S. Pat. No. 4,363,289 (corres. to the Published European Patent Application No. 0026538). The U.S. Patent relates to a method and an apparatus for applying an emulsion onto a screen-printing plate in which squeegees arranged at either side of the screen are advanced toward the screen face so as to make contact therewith the screens are inclined to allow emulsion to flow out of the squeegees at their front edges. The squeegees, are vertically moved relative to the screen. The emulsion flows down naturally from the squeegees so that the emulsion may be scraped by the front edge of the squeegee upon its upward movement for providing a uniform film thickness, but upon its downward movement (necessary for thick application) the emulsion flows into the underside of the squeegee and is applied in different quantities thereby which results in an irregular thickness. In applying emulsion on both sides of the screen starting at a lower section, a certain distance between the screen face and the front edges of the squeegees is needed in order to provide a relatively thick emulsion film because the contacted squeegees may scrape off the applied emulsion. Thus, a screen with a greater thickness of the emulsion on its printing side can not be produced. Furthermore, the squeegees on both sides of the screen are symmetrically and synchronously moved with each other by a single cylinder, so that one of the squeegees must be replaced by either a rod or roller for single side application of the screen, thereby requiring a troublesome replacement and resulting in a very difficult switchover between the application on both sides to single side application or vice versa through continuous and automatic operation. Upon printing with the screen, the application of a thicker emulsion on the printing side rather than on the ink-applying side is essential for obtaining a beautiful print and presents a difficult which is present in the prior art as described hereinabove.
Furthermore, another method has hitherto been employed in which an applying film having layered thereon a predetermined thickness of an emulsion is releasably coated on a substrate to form an emulsion film. The emulsion film in turn is set horizontally under a screen face, and a suitable squeegee is used for manually coating the applying film on the screen face in order to release the emulsion and release it from the screen through the action of a penetrating agent, such as water. In this method, however, the manual movement of the squeegee provides nonuniform penetration of the agent into the whole area of the applying film so as to leave non-attached portions thereon after the operation, so that a skillful applying operation is required.
Accordingly, an object of the invention is to solve the problem in the prior method and apparatus and to provide a method and an apparatus capable of variably determining a thickness of an emulsion on a printing face of a screen by selecting a thickness of an applying film, an applying pressure of a squeegee for feeding a penetrating agent onto the applying film, a feeding rate of the penetrating agent, and a type of the penetrating agent, and further providing uniform and sharp lines upon printings.